cost/benefit of some src.conf options

[Chris]

On 2021-03-26 12:17, Andrea Venturoli wrote:
> On 3/26/21 7:46 PM, Dimitry Andric wrote:
> 
>> That said, the retpoline mechanisms tend to be fairly well tested by
>> now, but will still have a non-negligible performance impact, maybe even
>> a large impact, depending on your workload. There is no simple answer
>> here, you will have to measure it for yourself.
> 
> AFAIK:
> _ RETpoline is an alternative to IBRS;
> _ the impact of RETpoline should be lower than IBRS;
> _ IBRS is enabled by default.
> 
> Did I get it wrong?
My understanding is that retpoline is really only of interest if your box 
might
accessed *locally* by *untrusted* individuals. See:

https://nvd.nist.gov/vuln/detail/CVE-2017-5715

--Chris
> 
> So, unless someone is willing to disable IBRS and live without mitigation, 
> it
> would be interesting to know how performance differs between the two.
> I've seen IBRS's impact on bhyve-hosted Windows guests reach 15%-20%.
> I've never tried RETpoline for the lack of information WRT to its stability: 
> I
> guess "fairly well tested" does not mean "production ready", or it would be
> enabled by default, wouldn't it? :)
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